Development and Testing of Membrane Biological Wastewater Processors

Ground-based laboratory and closed-chamber human tests have demonstrated the ability of microbial-based biological processors to effectively remove carbon and nitrogen species from regenerable life support wastewater streams. Application of this technology to crewed spacecraft requires the development of gravity-independent bioprocessors due to a lack of buoyancy-driven convection and sedimentation in microgravity. This paper reports on the development and testing of membranebased biological reactors and addresses the processing of planetary and International Space Station (ISS) waste streams. The membranes provide phase separation between the wastewater and metabolically required oxygen, accommodate diffusion-driven oxygen transport, and provide surface area for microbial biofilm attachment. Testing of prototype membrane bioprocessors has been completed. A two-thirds-person bioprocessor operated for 187 days and demonstrated 95% TOC reduction and 50% conversion of influent urea-nitrogen to nitrogen gas. A two-person system operated continuously for more than one year and averaged 93% TOC reduction. Ninetyfive percent of the TOC reduction was achieved in the first half (30 liters) of the system. On average, 4.5 mg of NO₃ was required for each mg of TOC removed. Based upon visual estimation, biomass accumulation was greatest in the initial third of the reactor volume. There was significantly less biomass in the remaining two-thirds of the system. Module change-out or back-flushing due to solids accumulation was not required for the duration of the test.